Photochromic Hydrogel Research Articles

Fabrication of novel MoOx / PVA hydrogel nanocomposite for photochromic smart window

Photochromic smart windows allow for simple manufacturing without the need for additional energy input for adaptive control of sunlight, which will have a huge impact on the comfort of daylight and the development of smart windows. Among them, although molybdenum-based materials have advantages such as low cost and stable coloring, the lack of fast transmission switching capability and liquid phase color changing environment limit its implementation in the field of smart windows. Here, we report a low-cost method to fabricate a novel photochromic hydrogel (MoOx/PVA) by combining molybdenum oxide nanosheets (MoOx, 2≤x≤3) with polyvinyl alcohol (PVA) gel. Under ultraviolet light (UV=360∼400 nm) irradiation, the hydrogel achieves rapid color change visible to the naked eye within 10 s, with an exponential decrease in transmittance, reversible switching of transparency between 70% and 5%, and retains about 95% transmittance after 14 cycles. Due to the good biocompatibility of molybdenum oxide, hydrogel can also be used for personal wearable, which can achieve 1.4°C of cooling when exposed to sunlight for 3 min. Moreover, the photochromic and recovery properties of the large-sized (29.7 cm×21 cm) MoOx/PVA hydrogel demonstrate its broad prospects for production applications in smart windows. It is believed that this study will open new opportunities for both fabrication and application in photochromic smart windows and intelligent devices.

Polyacrylamide/sodium alginate/sodium chloride photochromic hydrogel with high conductivity, anti-freezing property and fast response for information storage and electronic skin

Photochromic hydrogels have promising prospects in areas such as wearable device, information encryption technology, optoelectronic display technology, and electronic skin. However, there are strict requirements for the properties of photochromic hydrogels in practical engineering applications, especially in some extreme application environments. The preparation of photochromic hydrogels with high transparency, high toughness, fast response, colour reversibility, excellent electrical conductivity, and anti-freezing property remains a challenge. In this study, a novel photochromic hydrogel (PAAm/SA/NaCl-Mo7) was prepared by loading ammonium molybdate (Mo7) and sodium chloride (NaCl) into a dual-network hydrogel of polyacrylamide (PAAm) and sodium alginate (SA) using a simple one-pot method. PAAm/SA/NaCl-Mo7 hydrogel has excellent conductivity (175.9 S/cm), water retention capacity and anti-freezing properties, which can work normally at a low temperature of −28.4 °C. In addition, the prepared PAAm/SA/NaCl-Mo7 hydrogel exhibits fast response (<15 s), high transparency (>70 %), good toughness (maximum elongation up to 1500 %), good cyclic compression properties at high compressive strains (60 %), good biocompatibility (78.5 %), stable reversible discolouration and excellent sensing properties, which can be used for photoelectric display, information storage and motion monitoring. This work provides a new inspiration for the development of flexible electronic skin devices.

Ion-Cross-Linked Hybrid Photochromic Hydrogels with Enhanced Mechanical Properties and Shape Memory Behaviour.

Shape-shifting polymers usually require not only reversible stimuli-responsive ability, but also strong mechanical properties. A novel shape-shifting photochromic hydrogel system was designed and fabricated by embedding hydrophobic spiropyran (SP) into double polymeric network (DN) through micellar copolymerisation. Here, sodium alginate (Alg) and poly acrylate-co-methyl acrylate-co-spiropyran (P(SA-co-MA-co-SPMA)) were employed as the first network and the second network, respectively, to realise high mechanical strength. After being soaked in the CaCl2 solution, the carboxyl groups in the system underwent metal complexation with Ca2+ to enhance the hydrogel. Moreover, after the hydrogel was exposed to UV-light, the closed isomer of spiropyran in the hydrogel network could be converted into an open zwitterionic isomer merocyanine (MC), which was considered to interact with Ca2+ ions. Interestingly, Ca2+ and UV-light responsive programmable shape of the copolymer hydrogel could recover to its original form via immersion in pure water. Given its excellent metal ion and UV light stimuli-responsive and mechanical properties, the hydrogel has potential applications in the field of soft actuators.

Photochromic cellulose nanofibers-reinforced polyacrylic acid self-healable hydrogel toward dual-mode security authentication stamp

Photochromic inks have displayed various disadvantages such as poor durability, high cost and limited efficiency. The self-healing inks have shown to be more durable and photostable. In order to create an authentication stamp, UV-induced photochromic hydrogel inks with self-healable capabilities were developed. Nanoparticles of rare-earth aluminate (NREA) were synthesized and dispersed in a combination of cellulose nanofibers (CNF) and polyacrylic acid (PAA) to create an organic-inorganic hybrid ink. NREA were produced and analyzed using transmission electron microscope (TEM), revealing diameters of 1–4 nm. CNF were synthesized to act as a nanofiller and dispersing agent to improve the mechanical strength of the polyacrylic acid bulk and to prevent the agglomerates of the NREA. In order to create transparent prints, NREA must be uniformly disseminated in the CNF/PAA hybrid hydrogel ink without clumping. A paper surface was effectively stamped with the photochromic ink, and then the ink was thermofixed. Transparency was achieved by direct stamping of a consistent photochromic layer on the sheet surface, and this film was shown to become green when exposed to ultraviolet light as verified by photoluminescence spectral and CIE Lab analysis. The luminous paper sheets had an emission wavelength at 519 nm when irradiated at 368 nm. Energy-dispersive X-ray (EDX), infrared spectroscopy (FT-IR), X-ray fluorescence and scanning electron microscope (SEM) were utilized to examine the morphology of the stamped sheets. The cellulose nanofibers displayed diameters of 9–17 nm. The printed hydrogel ink displayed highly reversible photochromic emission without fatigue. Mechanical testing of the printed sheets and examination of the rheology of the luminous hydrogel was explored. The current NREA@CNF/PAA hydrogel ink offers a competent method for anticounterfeiting that can be used in a variety of authentication industries.

Photochromic performance of hydrogel based on deep eutectic solvent induced water soluble Cu-doped WO3 hybrids with antibacterial property

A novel fast photoresponse and self-fading photochromic hydrogel system was fabricated based on Cu-doped WO 3 , which prepared by employing DESs as co-solvent. The photochromic hydrogel displayed remarkable antibacterial ability and non-cytotoxicity, great potential in the applications of stimuli-responsive materials such as smart windows, repeatable erasing paper and photochromic sensors. • Deep eutectic solvents (DESs) as a green co-solvent was employed to prepare Cu-doped WO 3 photochromic materials with excellent water solubility. • The fabricated P(AM-HEA)-Cu-WO 3 -X photochromic hydrogels exhibit rapid photoresponse and enhanced self-fading rate. • The deep-blue colored P(AM-HEA)-Cu-WO 3 -25% hydrogel could come back to its original colorless state within 40 min. • The mechanism of photochromic and self-fading behaviors for P(AM-HEA)-Cu-WO 3 -X photochromic hydrogels was detailed analyzed. • The remarkable antibacterial performance and cell viability possessed in hydrogels also confirmed. A novel photochromic and self-bleaching hydrogel was prepared based on the Cu-doped tungsten oxide (WO 3 ) hybrid encapsulated in the co-polymer matrix polymerized using acrylamide (AM) and hydroxyethyl acrylate (HEA) as monomers. The Cu-WO 3 -25% hybrid was generated by introducing Cu species into the lattice of WO 3 with hexagonal-like prismatic structure and acted as light absorber. Given that WO 3 and Cu-doped WO 3 hybrids possess superior water solubility by using water and deep eutectic solvents (DESs, ChCl:EG) containing sufficient hydrogen bond as co-solvent, the high transparency of 90% of the hydrogels was achieved. As compared with P(AM-HEA)-WO 3 -based hydrogel, the P(AM-HEA)-Cu-WO 3 -X hydrogel exhibited the enhanced coloration degree under UV irradiation. The P(AM-HEA)-Cu-WO 3 -25% photochromic hydrogel changed from colorless to blue immediately once illuminated by UV light, and turns into dark-blue with the irradiation time going on. The self-bleaching process indicates it only takes 40 min for the P(AM-HEA)-Cu-WO 3 -25% hydrogel to return to the original colorless transparent state. Furthermore, the hydrogel systems exhibit efficient antibacterial activities against bacteria of both E. coli and S. aureus , accompanying with outstanding biocompatibility. As such, the fabricated hydrogel demonstrates rapid photoresponse, self-bleaching process, superior antibacterial performance, and cell viability, showing a great potential application as stimuli-responsive materials.

Synthesis of sodium alginate/polyacrylamide photochromic hydrogels with quadruple crosslinked networks.

Photochromic hydrogels have great potential for inkless printing, smart display devices, anti-counterfeiting and encryption. However, the short information storage time limits their large-scale application. In this study, a sodium alginate/polyacrylamide photochromic hydrogel with ammonium molybdate as the color change factor was prepared. The addition of sodium alginate was beneficial to the improvement of the fracture stress and elongation at break. In particular, when the content of sodium alginate was 3%, the fracture stress increased from 20 kPa without sodium alginate to 62 kPa. Different photochromic effects and information storage times were achieved by regulating the calcium ion and ammonium molybdate concentration. And the hydrogel with an ammonium molybdate immersion concentration of 6% and calcium chloride immersion concentration of 10% can store information for up to 15 h. At the same time, the hydrogels were able to maintain their photochromic properties over five cycles of "information writing - erasure" and achieved "hunnu" encryption. Therefore, the hydrogel shows excellent information controllable erasure properties and encryption functions, indicating its broad application prospects.

Construction of a novel self-bleaching photochromic hydrogel embraced within the Zn-MOF@WO3 junction for assembling UV-irradiated smart rewritable device

Photochromic hydrogels, which are dynamic in response to external light stimuli, have aroused increasing attentions due to their potential applications in intelligent devices. However, achieving excellent photochromic activity with fast photoresponse and self-bleaching rates still remains a huge challenge. Herein, a novel photochromic junction of zinc-based metal–organic framework (Zn-MOF) and tungsten oxide (WO3) was established as photochromic unit and embraced within hydrogel of poly(acrylic acid-co-polyethylene glycol) [P(AA/PEG)] via the interaction of ionic and hydrogen bonding (denoted as P(AA/PEG)-Zn-MOF@WO3), following by exploiting as self-bleaching photochromic agent for assembling UV-irradiated smart rewritable device. The photoinduced electrons can be efficiently separated and migrated from Zn-MOF to WO3 in the Zn-MOF@WO3 junction after UV irradiation, thereby increasing the coloration degree. Due to the enhanced fast response to light stimuli, the P(AA/PEG)-Zn-MOF@WO3-3 hydrogel prepared using 200 mg Zn-MOF demonstrated the fast responsive photochromic behavior of 10 s under UV lamp illumination and the self-fading process could be easily performed in room condition (within 20 min). Moreover, the coloration degree of P(AA/PEG)-Zn-MOF@WO3-3 photochromic hydrogel was precisely controlled and repeated by changing the UV irradiation time. Consequently, the fast photochromic and self-fading properties of P(AA/PEG)-Zn-MOF@WO3-3 afforded rapid and easy ‘‘writing’’ and “erasing” abilities. The present work proposes a new way for the construction of the reversibly responsive photochromic hydrogel with smart optical materials, further broadening their applications in intelligence sensors, smart windows, and flexible memory devices.

Polyacrylamide/sodium alginate photochromic hydrogels with enhanced toughness and fast response for optical display and rewritable information record

Photochromic hydrogels have broad prospects in wearable optoelectronic technology, rewritable information storage technology, biological imaging agents and chemical sensors, etc. However, it is still a challenge to develop photochromic hydrogels with high transparency, mechanical properties, fast response, stability and color reversibility. In this study, a novel photochromic hydrogel (PAAm/SA-Mo7) was prepared by loading ammonium molybdate (Mo7) into a double-network hydrogel of polyacrylamide (PAAm) and sodium alginate (SA) through a facile one-step method. The introduction of SA and Mo7 significantly improved the mechanical properties of hydrogels, and the maximum elongation and breaking energy are 27.5 and 86 times higher than those of pure PAAm. Furthermore, the photochromic hydrogels have fast response and stable reversible color change. The coloring process of hydrogels can be precisely controlled by the time and intensity of UV irradiation, and the fading process can also be controlled by temperature. The photochromic hydrogel can be applied to self-erasing rewritable media and information storage. This work provides a new approach for the development of flexible wearable optoelectronic materials.

Real-Time Quantitative Detection of Ultraviolet Radiation Dose Based on Photochromic Hydrogel and Photo-Resistance

Real-Time Quantitative Detection of Ultraviolet Radiation Dose Based on Photochromic Hydrogel and Photo-Resistance

Gradient dynamic cross-linked photochromic multifunctional polyelectrolyte hydrogels for visual display and information storage application

The homogeneous distribution of organic photochromic materials in the network can endow hydrogels with excellent photochromic properties, but many weaknesses, such as the poor mechanical properties and short service life, limit their further development in the field of visual display and information storage devices. To solve this problem, a novel photochromic polyelectrolyte hydrogel with excellent mechanical, conductive, self-healing and adhesive properties has been designed and prepared based on a triple gradual ionic-hydrogen bonds network through a unique buffer band-like structural programming method. In the hydrogel system, naphthoprans was attached to the polymer chains by hydrogen bonding to achieve remarkable photochromic efficiency and color rendering (photochromic time <4.5s). The unique photochromic hydrogel network with buffer band-like structure is programmed by introducing ionic and hydrogen bonds with gradient strength between polyelectrolyte polymer chains into the structure. The specific type and strength of interactions between polymer units were evaluated via the density functional theory (DFT) calculations. Such unique network endowed the photochromic hydrogel with considerable mechanical property (tensile strength >1.00 MPa, compressive strength >17.00 MPa), superior self-healing ability (healing time <30min, healing efficiency >90%), conductivity (6.72 × 10−3 S/cm), adhesive property and pH sensitivity. These excellent characteristics of the photochromic multifunctional polyelectrolyte hydrogel make it interesting candidates for visual displays and information storage devices.

A Multi‐Functional and Rapid Responsive Photochromic Hydrogel for UV Indicators

AbstractUltraviolet rays can cause serious damage to the skin and eyes, and in severe cases, it may lead to skin cancer. Therefore, the prediction, real‐time monitoring, and protection of ultraviolet rays is an important aspect of scientific research. Herein, a novel photochromic hydrogel is developed by using acrylic acid (AA) and 2‐(dimethylamino) ethyl methacrylate (DMAEMA) as the cross‐linking agent for hydroxyethyl methacrylate (HEMA) with the addition of microcrystalline 2,2‐diphenyl‐2H‐naphtho[1,2‐b] pyran‐6‐carbaldehyde (NP) for the real‐time monitoring and protection against ultraviolet rays. The binding mechanism of AA and DMAEMA is predicted using density functional theory (DFT). Also, the designed photochromic hydrogels exhibit excellent properties of pH and temperature sensitivity, rapid responsiveness, self‐healing, pressure resistance, high transparency, and electrical conductivity. The optical performance indicate that the photochromic hydrogel has a fast response to ultraviolet rays with color change occurring in 0.5 s and maximum color development in 5 s. In addition, the hydrogels show excellent compression resistance, and their residual stress decrease by only 0.85% after five cycles of compression. Therefore, it is hypothesized that the multi‐induction of these soft photochromic hydrogels could be applied in wearable devices, information storage equipment, display devices, and light printing.

High-Performance Photochromic Hydrogels for Rewritable Information Record.

Rewritable information record materials usually demand not only reversibly stimuli-responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super-strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion-hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22MPa, work of tension of 12.8MJ m-3 , and modulus of elasticity of 8.6MPa. Moreover, the SP-based Ca2+ crosslinked hydrogels can be enhanced further when exposed to UV-light via ionic interaction coordination between Ca2+ , merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices.

Synthesis and characterization of novel photochromic and pH-sensitive colorimetric hydrogel based on azobenzene

This article reports the synthesis of new Dye A from the reaction of 4-methyl 2-nitroaniline, NaNO2/H+, and sodium 1-naphtholate. Dye A responded with an obvious colour change visible to naked eyes to pH, ultraviolet light, and fluoride ion and was studied by UV–vis spectroscopy. Next, the reaction of Dye A with crotonic anhydride leads to the formation of MDye A. Subsequently, synthesis of a new type of photochromic and pH-sensitive colorimetric hydrogel consisting of a new azobenzene (MDye A), acrylic acid, acrylamide, N,N'-methylenebisacrylic amide as a crosslinking agent, and sodium acrylate in the presence of 2,2′-azobis(isobutyronitrile) as initiator and sorbitan monostearate (Span 60) as the dispersant or under a LED lamp (400 nm, 20 W) in the presence of CdS nanorods and β-cyclodextrin was studied. The products were characterized using 1H NMR,13C NMR, TGA, DTG, SEM, TEM, and FTIR spectroscopy. The synthesized new hydrogel showed good pH responsiveness and photoresponsiveness, which was investigated by UV–vis spectroscopy. Also, the effects of parameters such as amounts of CdS nanorods, cross-linker, and water, duration of pre-oxygenation, light intensity on the swelling of gel, and polymerization rate in the synthesis of hydrogel were investigated.

Sunlight-driven photochromic hydrogel based on silver bromide with antibacterial property and non-cytotoxicity

A novel photochromic hydrogel system was designed and fabricated based on silver bromide and cuprous bromide in poly(hydroxyethyl acrylate-co-polyacrylamide) hydrogel matrix. The first time we overcome the atoms side reaction and migration of halides in opening hydrogel system to realize photochromism. Here, polyvinyl pyrrolidone (PVP) and glycerol were employed as a surfactant and sustainable co-solvent, respectively, whose synergistic effect make AgBr endows the hydrogel with photochromic stability and repeatability. The photochromic hydrogel can be changed reversibly between light-blue and brown color for least 15 times in air under a simulated solar light irradiation. Both UV–vis absorption (approximately 408 nm) and the valence states of the metal ions were studied and verified the conversion between Ag+ and Ag0. The process of color changing was studied and the fabricated hydrogel with a half-life fading period (t1/2) was 6.78 min under a simulated solar light irradiation. Reasonably, the as-fabricated photochromic hydrogel displayed remarkable antibacterial ability to both Gram-positive- and Gram-negative bacterium with the Ag ions in the system. Interestingly, due to the little dosage of AgBr and CuBr in the hydrogel, it also possessed excellent non-cytotoxicity property to L929 Mouse Fibroblast cells. Since its excellent photochromic and biological properties, the hydrogel has potential applications in the field of smart materials such as photochromic contact lenses, sensors and artificial intelligent devices or bionic skin.

Highly transparent and stretchable hydrogels with rapidly responsive photochromic performance for UV-irradiated optical display devices

Photochromic hydrogels have attracted considerable attention owing to their potential application in optical devices. However, the weak mechanical properties severely limited their applications. Here, a novel photochromic hydrogel with high transparency, high stretchability and rapid photochromic responsiveness has been successfully designed and prepared by introducing a redox photochromic material (Mo) into the hybrid hydrogel. The photochromic hydrogel with rapid photochromic response achieved discoloration process within only 3 s and the fading process could be easily performed under the air environment. Moreover, the ability to rewrite and erase optical information have been implemented on the photochromic hydrogels. Therefore, this strategy of photochromic hydrogel would contribute to design a new generation of optical display devices.

Two-dimensional tungstate nanosheets for constructing novel photochromic hydrogel with ultrahigh flexibility

A hydrogel possessing interesting photochromic behaviors was developed by in situ ultraviolet (UV) irradiation–assisted polymerization of an aqueous solution of N-isopropylacrylamide monomer in the presence of cesium tungstate nanosheets. By this process, a hierarchical porous network structure was finely constructed while showing ultrahigh flexibility. More importantly, the newly prepared hydrogel retained the photochromic properties of the cesium tungstate nanosheets. The color transitions could be readily controlled by UV laser irradiation and were completely reversible via laser exposure or dark treatment. The nanocomposite hydrogel with its excellent photochromic properties and ultrahigh flexibility will have great applications in flexible photochromic devices. The synthetic procedure is simple and has promises to be extended to developing other hydrogels with various new functionalities.

Low-Cost, Rapidly Responsive, Controllable, and Reversible Photochromic Hydrogel for Display and Storage.

Traditional optoelectronic devices without stretchable performance could be limited for substrates with irregular shape. Therefore, it is urgent to explore a new generation of flexible, stretchable, and low-cost intelligent vehicles as visual display and storage devices, such as hydrogels. In the investigation, a novel photochromic hydrogel was developed by introducing the negatively charged ammonium molybdate as a photochromic unit into polyacrylamide via ionic and covalent cross-linking. The hydrogel exhibited excellent properties of low cost, easy preparation, stretchable deformation, fatigue resistance, high transparency, and second-order response to external signals. Moreover, the photochromic and fading process of hydrogels could be precisely controlled and repeated under the irradiation of UV light and exposure of oxygen at different time and temperature. The photochromic hydrogel could be considered applied for artificial intelligence system, wearable healthcare device, and flexible memory device. Therefore, the strategy for designing a soft photochromic material would open a new direction to manufacture flexible and stretchable devices.

A rapidly responsive photochromic hydrogel with high mechanical strength for ink-free printing

We report a hydrogel with excellent mechanical strength and rapid photochromism that can be used for ink-free printing.

Synergistic effect of sunlight induced photothermal conversion and H2O2 release based on hybridized tungsten oxide gel for cancer inhibition.

A highly efficient photochromic hydrogel was successfully fabricated via casting precursor, which is based on amorphous tungsten oxide and poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide). Under simulated solar illumination, the hydrogel has a rapid and controlled temperature increasing ratio as its coloration degree. Localized electrons in the amorphous tungsten oxide play a vital role in absorption over a broad range of wavelengths from 400 nm to 1100 nm, encompassing the entire visible light and infrared regions in the solar spectrum. More importantly, the material exhibits sustainable released H2O2 induced by localized electrons, which has a synergistic effect with the rapid surface temperature increase. The amount of H2O2 released by each film can be tuned by the light irradiation, and the film coloration can indicate the degree of oxidative stress. The ability of the H2O2-releasing gels in vitro study was investigated to induce apoptosis in melanoma tumor cells and NIH 3T3 fibroblasts. The in vivo experimental results indicate that these gels have a greater healing effect than the control in the early stages of tumor formation.

Preparation and characterization of a photochromic hydrogel

A new type of photochromic hydrogel, spiropyran (SP)-Polyvinylpyrrolidone (PVP)-poly (N-isopropyl acrylamide) (PNIPAM) hydrogel with functionalized SP chemically incorporated, was synthesized. The molecular structure of synthesized products was given by nuclear magnetic resonance (NMR) spectra and infrared spectrum (IR). The photochromism of the hydrogel was evidenced by photography and characterized by ultraviolet-visible (UV-Vis) spectroscopy. The photochromic reversibility of the hydrogel was tested through observing its responses to the alternating UV irradiation to dark environment. The fluorescence micrographs showed the fluorescent effect as well as confirmed the photochromic properties of the hydrogel, and indicated that the chemical incorporation made the functionalized SP distribute well in the gel. Copyright © 2011 VBRI press.